Field emission devices have potential applications in flat panel displays. Field emitters used in flat panel displays must be stable, long lasting and should have a relatively uniform emission over the surface of the display.
Carbon nanotubes are very small tube-shaped molecules having the structure of a graphite molecule rolled into a tube. Carbon nanotubes are electrically conductive along their length, chemically stable, and can have very small diameters (much less than 100 nanometers) and large aspect ratios (length/diameter). Due to these properties and other properties, it has been suggested that carbon nanotubes can be used as field emission devices.
However, it has been unclear how to realize a field emission device exploiting carbon nanotubes. They are difficult to work with in bulk, and, on a microscopic level, often form an impossibly tangled mess resembling a hairball. To produce a useful field emission device for flat panel displays, the carbon nanotubes should be patterned into individual field emitters. A problem with present methods of making carbon nanotube field emitters is that it is not clear how to pattern the carbon nanotube to provide arrays of emitters.
U.S. Pat. No. 5,773,921 to Keesman et al. discloses a field emission device which employs sharp-edged graphite wafers. Carbon nanotubes are disposed on the sharp edge of the graphite wafers and help to increase field emission. The carbon nanotubes are disposed on the graphite wafers by sputtering a nearby graphite target. The carbon nanotubes are not aligned in any way.
U.S. Pat. No. 4,272,699 to Faubel et al. discloses an ion source which uses carbon fiber field emitters. The carbon fibers are bundled together and an electric field is applied to the bundle. The carbon fibers are held by a macroscopic mechanical device that holds the fibers parallel. Such a mechanical device cannot be used with carbon nanotubes, which are orders of magnitude smaller than the carbon fibers used by Faubel et al.
U.S. Pat. No. 5,773,834 to Yamamoto et al. describes a method of making carbon nanotubes on the surface of a carbon-containing substrate by ion bombardment. The carbon nanotubes produced can be used as field emitters. The carbon nanotubes produced according to Yamamoto are not aligned, and in particular, are not aligned perpendicular to the substrate. Also, Yamamoto does not disclose how to pattern the substrate to provide individual field emitters.
Yet another problem with present methods for making carbon nanotube field emitters is that scale-up to large wafers is difficult or not possible.
There exists a need in the art for a method of producing aligned carbon nanotubes. In particular, such aligned carbon nanotubes can be used as superior field emission devices.